1. Field of the Invention
This invention relates to a transition duct for a gas turbine engine, specifically to a novel and improved profile for a transition duct that results in lower operating stresses and extended component life.
2. Description of Related Art
In a typical can annular gas turbine engine, a plurality of combustors are arranged in an annular array about the engine. The combustors receive pressurized air from the engine""s compressor, adds fuel to create a fuel/air mixture, and combusts that mixture to produce hot gases. The hot gases exiting the combustors are utilized to turn a turbine, which is coupled to a shaft that drives a generator for generating electricity.
The hot gases are transferred from the combustor to the turbine by a transition duct. Due to the position of the combustors relative to the turbine inlet, the transition duct must change cross-sectional shape from a generally cylindrical shape at the combustor exit to a generally rectangular arc-like shape at the turbine inlet. In addition, the transition duct undergoes a change in radial position, since the combustors are typically mounted outboard of the turbine. Extreme care must be taken with respect to the design of these geometric transitions to avoid sharp geometric changes, otherwise regions of high stress and stress concentrations can occur. The combination of complex geometry changes as well as extreme mechanical and thermal loading seen by the transition duct create a harsh operating environment that can lead to premature deterioration, requiring repair and replacement of the transition ducts. To withstand the hot temperatures from the combustor gases, transition ducts are typically air-cooled. A variety of methods are available to provide cooling such as through internal channels, impingement cooling, or effusion cooling. Severe cracking has been known to occur in transition ducts having extremely sharp geometry changes and internal air-cooled channels.
The present invention seeks to overcome the shortfalls of the prior art by providing a transition duct having a geometric profile optimized to eliminate areas having high stress concentrations and high steady and vibratory stresses while still transferring the hot combustion gases from the combustor to the turbine inlet in an acceptable manner.
In accordance with the present invention, there is provided a novel and improved transition duct having an enhanced profile and other characteristics for improved performance and enhanced durability. To accomplish this, the internal flowpath geometry of the transition duct has been optimized to remove areas of sharp geometric change. The sharp geometric changes in combination with high thermal and mechanical loading, caused regions of high steady and vibratory stresses and local stress concentrations can lead to cracking and premature failure of the transition duct. The internal flowpath of the transition duct has been optimized to provide a more homogeneous temperature profile of the hot combustion gases to the turbine as well as to raise the natural frequency of the transition duct. Providing a more homogeneous temperature profile to the turbine inlet helps to minimize the distress to the first stage of the turbine.
A variety of cooling methods can be used in combination with the enhanced profile of the present invention transition duct. In the preferred embodiment, the cooling system continues to use air, but the air is directed through a plurality of effusion holes in the panel assembly of the transition duct. Effusion cooling provides more uniform cooling of the transition duct than the plurality of internal cooling channels used in the prior art and were a source of stress concentrations.
In the preferred embodiment of the present invention, there is provided a transition duct with a panel assembly having an inlet end of generally circular cross section and an outlet end having a generally rectangular arc-like cross section with an uncoated internal profile substantially in accordance with the coordinate values xcex8, X, Y, and Z as set forth in Table 1. The origin of the coordinate system is positioned at the center of the panel assembly inlet end along a centerline axis. It will be appreciated that the coordinate values given are for manufacturing purposes, in a room temperature condition. Each set of coordinate values X, Y, and Z in Table 1 is standard Cartesian coordinates, and each set corresponds to a specific sweep angle xcex8, which together define a cross section of the panel assembly. Each cross section is joined smoothly with adjacent cross sections to define a panel assembly for the transition duct. It will also be appreciated that as the transition duct transfers hot combustion gases from a combustor to the turbine inlet, the transition duct heats up and therefore the coordinates provided in Table 1 do not necessarily correspond to the panel assembly position when in operation at an elevated temperature.
In an alternate preferred embodiment, there is provided a transition duct with a panel assembly having an inlet end of generally circular cross section and outlet end having a generally rectangular arc-like cross section with an uncoated internal profile within an envelope of +/xe2x88x920.250 inches in a direction normal to any surface of the panel assembly substantially in accordance with the coordinate values xcex8, X, Y, and Z as set forth in Table 1. The origin of the Cartesian coordinate system is positioned at the center of the panel assembly inlet end along a centerline axis. A distance of +/xe2x88x920.250 inches in a direction normal to any surface location along the panel assembly defines an envelope for this particular panel assembly and ensures that manufacturing tolerances are accommodated within the envelope of the panel assembly. As with the first preferred embodiment, it will be appreciated that the coordinate values given are for manufacturing purposes, in a room temperature condition. Each set of coordinate values X, Y, and Z in Table 1 is in standard Cartesian coordinates, and each set corresponds to a specific sweep angle xcex8, which defines a cross section of the panel assembly. Each cross section is joined smoothly with adjacent cross sections to define a panel assembly for the transition duct. It will also be appreciated that as the transition duct transfers hot combustion gases from a combustor to the turbine inlet, the transition duct heats up and therefore the Cartesian coordinates for a given xcex8 value provided in Table 1 may not necessarily correspond to the panel assembly position when in operation at an elevated temperature.
It is an object of the present invention to provide a novel, optimized internal profile for a panel assembly of a gas turbine transition duct having improved robustness and extended life.
It is another object of the present invention to provide a novel and optimized internal profile for a panel assembly of a gas turbine transition duct having an envelope for the profile defining manufacturing tolerances.